1. Field of the Invention
This invention relates to room temperature vulcanizable silicone elastomeric compositions in organic solvent.
2. Description of the Prior Art
Silicone elastomers which cure at room temperature have been known for some time. Such elastomers have been prepared by using crosslinking systems which cure upon mixing the ingredients, such compositions are stored in two or more containers; and by using crosslinking systems which are stable in the absence of moisture but which cure upon exposure to moisture, such compositions are storable in a single container. The first type are usually packaged in at least two containers and are put to use by mixing the contents of the two containers whereas the second type are packaged in one container which seals out atmospheric moisture and are used merely by removing the contents of the container and permitting it to come into contact with the atmosphere.
One type of silicone elastomer which is stored in two containers and which cures upon mixing a hydroxylated organosiloxane, an alkyl polysilicate and a metal carboxylate is well known as described by Polmanteer in U.S. Pat. No. 2,927,907.
A one package room temperature vulcanizable silicone elastomeric composition which combines a hydroxylated organosiloxane, an acyloxysilane and a metal salt of a carboxylic acid is well known as described by Bruner in U.S. Pat. No. 3,077,465. These compositions described by Bruner are stable in the absence of moisture but cure when exposed to atmospheric moisture.
Hartlage in U.S. Pat. No. 3,642,692 describes a one package composition which is stable in the absence of moisture but cures to a silicone elastomer when exposed to moisture. The compositions described by Hartlage consist essentially of 100 parts by weight hydroxyl radical terminated polydiorganosiloxane having a viscosity of from 1,000 to 50,000 cs. at 25.degree. C., 0.5 to 15 parts by weight of EQU R'Si(OOCCH.sub.3).sub.3
where R' is methyl, ethyl, vinyl, n-propyl, isopropyl, n-butyl, isobutyl, amyl and phenyl and 0.5 to 5 parts by weight of an ethoxylated compound selected from tetraethoxysilane and ethylpolysilicate. These compositions of Hartlage have improved cleanability compared to compositions which do not contain the ethoxylated compounds. The silicone elastomers obtained by Hartlage have durometers on the Shore A scale of about 28, a tensile of about 240 p.s.i., (pounds per square inch), an elongation of about 380 and a Die B tear strength of about 25 p.p.i. (pounds per inch).
It was unexpected that tougher silicone elastomers could be obtained by combining ethylpolysilicate and monoorganotriacetoxysilane in certain ratios as crosslinking agents to crosslink high viscosity hydroxylated polydimethylsiloxane in an organic solvent.